Changed Alternator, Now Have Coolant Problem!

Changed my alternator, while doing that I checked and cleaned off some corroded wires and connections, after I put the new alternator on and fired the stang back up. just a few miles later my MIL light comes on, read codes and got one
P0118 - ENGINE COOLANT TEMPERATURE CIRCUIT HIGH INPUT
I also noticed that my factory temp gauge is not working now.

Im only putting out 13.0 volts max at highway speeds due to pully swap, so excessive volts is not causing it.

Would changing out the sensor fix this?
I triple checked everything and it appears nothing is disconnected.

I did a search but couldn't find anything.

THANKS IN ADVANCE
-Chris

2000 GT